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The Newsletter of Cox Metalworks and Superior Tray Systems

THERMAL EXPANSION:Environmental considerations for cable bus design.

pg.1

CABLE TRAY:New features improve ease of installation.

pg.3

THERMAL EXPANSION DESIGN IN CABLE BUS

Today’s large scale infrastructure projects come with their own set of unique challenges. One such challenge that must be considered is the impact of thermal expansion. The facts of the matter are simple: construction materials contract and expand over their operating temperature range. We are familiar with expansion joints in bridges, and expansion fittings in long pipe runs. These are examples of situations in which engineers have developed techniques to ensure a long and maintenance free lifetime. Likewise, so to have specialized techniques been developed to account for thermal expansion in large scale cable bus systems.

Continued page 2...Thermal expansion poses a unique challenge for large infrastructure projects

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Expansion joints allow a cable bus housing to expand in a controlled manner. Considering a 100m cable bus system under normal site conditions, an Aluminum housing would expand 18cm. A Stainless Steel housing would expand only 8cm. In the absence of expansion joints, this would put an undue stress on the support structures and connected equipment. Under these same conditions, the copper conductor of the power cables would expand 14cm. Special fittings accommodate the difference in expansion between conductors and the cable bus housing. Proper design and placement of expansion joints and fittings can minimize stresses and ensure a long system life.

An additional environmental problem sometimes encountered

Thermal Expansion over 100m

Exp

ansi

on

(cm

)

0

5

10

15

20

Aluminum

Stainless Steel

Copper Note:Values based on typical temperature range of: -40°C to +40°C

is frost heaving. Under certain soil conditions underground ice can form, heaving the soil level by as much as 30cm. Often in road crossings, cable bus systems are installed in a pre-cast concrete trench. Here especially it is important to have hinged fittings to accommodate the potentially damaging effects of frost heave.

Disregarding these environmental impacts can have serious detrimental effects, and lead to disruptive system downtime. No matter how complex the situation, the design team at Superior Tray has the experience to develop long term solutions in even the most unforgiving environments.

Hinged fittings can accommodate a vertical offset in situations where frost heave would normally cause buckling.

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Cox Metalworks Inc.#2 13015 84th Avenue,Surrey, BC V3W 1B3604.572.4419www.coxmetalworks.com

Superior Tray Systems Inc.#2 13015 84th Avenue,Surrey, BC V3W 1B3604.572.4419www.superiortray.com

UNIQUE FEATURES:

Custom fittings and injection

moulded support blocks were

specially designed to facilitate

installation of the 230V power

cables.

POWER DAM SHOWCASES NEW CABLE TRAY FEATURES

A retrofit at a North Dakota power dam profited from new cable tray features provided by Superior Tray. These unique Superior Tray features matched the customer’s requirements where all other manufacturers fell short. The cable tray system was designed to support massive 230kV power cables, nearly 3x larger in size than a typical system. Custom molded support blocks were designed in a flame retardant V0 material. Finally, the complete system featured an interlocking shroud at every joint, including expansion joints. This

completely ensured the cables would be protected from damage.

In order to speed up installation, custom sections were supplied to follow bends in the cable tray layout. These custom fittings minimized stresses on the power cables, while eliminating the need to do any field cutting. Overall, the features provided by Superior Tray contributed to a system design that perfectly met the customer’s unique requirements.

Custom cable tray sections smoothly follow a 26’ tunnel bend radius